Acrylonitrile butadiene styrene (ABS) resins, thermoplastic resin compositions such as polycarbonate resins/ABS resins, or reinforced thermoplastic resin compositions prepared by reinforcing these thermoplastic resin compositions with inorganic fillers have been widely used as the housing materials of electronic devices such as laptop personal computers, liquid crystal projectors and portable devices. In general, as a method for producing a housing, an injection molding method in which the above resin compositions can be shaped freely to some extent has been employed.
In recent years, demands have increased for electronic devices to be thinner and more lightweight, and also to satisfactorily withstand the impacts and loads while being placed inside a bag or such containers. In order to satisfy these demands, the resin used for a housing has to have not only high rigidity and impact resistance, but also high drop impact resistance when the products are dropped.
Here, it has been known that the drop impact resistance when the products are dropped is highly correlated with the surface impact strength measured by a falling ball test in accordance with the UL1950 standard or the like, while showing a relatively low correlation with the Izod impact strength or the Charpy impact strength. Therefore, the resin used for a housing is required to have high surface impact strength rather than high Izod impact strength or Charpy impact strength.
Among the conventionally used resin materials for housings of electronic devices, the ABS resins or polycarbonate resins/ABS resins that are not reinforced by inorganic fillers have low rigidity and could not meet the demands for thinning of electronic device housings in recent years.
In addition, although glass fiber-reinforced resin compositions may be used in some cases as resin materials for housings of electronic devices, the balance between the rigidity and the weight has not been satisfactory.
For this reason, carbon fiber-reinforced thermoplastic resin compositions are now being examined as housing materials for electronic devices.
However, although conventional carbon fiber-reinforced thermoplastic resin compositions exhibit high rigidity and the weights thereof can be reduced, they are problematic as a housing material since they are brittle and easily broken.
Thus, as a means to overcome these problems, a resin composition has been proposed in Patent Document 1, which contains an aromatic polycarbonate resin, a carbon fiber which has been surface-treated with a polyamide, and a lubricant having at least one functional group selected from a carboxyl group, a carboxylic acid anhydride group, an epoxy group and an oxazoline group.
In Patent Document 1, although the carbon fiber which is subjected to a surface treatment with a polyamide dissolved in methyl alcohol has been used, there is a description stating that a high impact resistance (Izod impact strength) cannot be achieved solely by the use thereof. In addition, the carbon fiber disclosed in Patent Document 1 does not improve the surface impact strength. Moreover, because the resin composition described in Patent Document 1 contains a lubricant, a large amount of gas was generated during molding, which is undesirable.
In addition, as a means different from that of Patent Document 1, a carbon fiber-reinforced polycarbonate resin composition has been proposed in Patent Document 2, which contains a polycarbonate resin, a rubber-containing polymer and a carbon fiber sized by a polyamide-based sizing agent. As the rubber-containing polymer disclosed in Patent Document 2, MBS resins containing (meth)acrylates having an alkyl group of 1 to 18 carbon atoms, butadiene and styrene as main materials or MAS resins composed of methacrylates, acrylates and styrene have been used. As a polyamide-based sizing agent, nylon 3, nylon 4, nylon 6, nylon 66 or the like has been used.
However, it was impossible for the carbon fiber-reinforced polycarbonate resin composition described in Patent Document 2 to improve the surface impact strength.